using LM324 as comparator

[Wida Lidia]

I am using LM324 as comparator. I wanted to make output voltage 5V when I receive signal greater than 4V but in fact I just got 3,7 V. My Vcc is 5 V. Whats the problem?

 

[FvM]

There's no problem with the part, the behaviour is according to LM324 specification. (You may want to review the datasheet).

You can try a pull-up resistor.

 

[dick_freebird]

A LM339 comparator is a better choice usually. You
might add a pullup resistor to give you higher VOH
from the op amp (same as you'd need for the '339).

 

[Wida Lidia]

why pull-up resistor can give me better output?

 

[FvM]

The answer is in the circuit. If you don't see it, just try. When pulling the output voltage above regular Vcc-1.1V saturation level, you are working against a 50 µA current source.